Catalyst with a mordenite base containing at least one metal of

Details Catalyst with a mordenite base containing at least one metal of Catalyst with a mordenite base containing at least one metal of

1991-10-16

1993-08-10

Dees, Carl F.

Catalyst, solid sorbent, or support therefor: product or process

Zeolite or clay, including gallium analogs

And additional al or si containing component

502 60, 502 74, 502 78, B01J 2918, B01J 2920

Patent

active

052348733

DESCRIPTION:

BRIEF SUMMARY
This invention relates to a catalyst of aluminosilicate type comprising an H-shaped mordenite whose geometric selectivity has been modified by deposition on the outside surface of its crystals of at least one metal selected from the metals of groups IIa (Be, Mg, Ca, Sr, Ba, Ra), IVb (Ti, Zr, Hf), IIb (Zn, Cd, Hg) and IVa (Ge, Sn, Pb) of the periodic table (Handbook of Chemistry and Physics, 61st edition, 1980-81), optionally at least one metal from group VIII of said table and a matrix and its use in the isomerization reactions of C8 aromatic hydrocarbons. It also relates to the process of preparation of said mordenite.
The catalysts now used industrially in these reactions are essentially based on zeolite ZSM5, by itself or in a mixture with other zeolites, such as mordenite, for example. These catalysts are described in particular in patents U.S. Pat. Nos. 4,467,129, 4,482,773 and EP-B-0138617.
The advantage of zeolite ZSM5 resides in its excellent selectivity of shape, which leads to a great selectivity of paraxylene, the selectivity relative to undesirable secondary dismutation reactions remaining at a very low level. The mordenite is a very active zeolite for the isomerization reaction of the C8 aromatic compounds, in particular more active than the ZSM5, however, it does not have special geometric selectivity properties. This is reflected, whatever its Si/Al ratio may be, by paraxylene selectivities lower than those obtained for zeolite MFI and particularly by very large productions of trimethylbenzene. The production of trimethylbenzene by dismutation is actually favored in the mordenite whose microporous system is more open than that of ZSM5: the openings are at 12 oxygens instead of 10 for ZSM5.
The applicant has discovered that it is possible, thanks to the deposition on the outside surface of the mordenite crystals of at least one metal selected from the metals of groups IIa, IVb, IIb and IVa and in particular of magnesium, titanium, zinc and/or tin, to obtain active and selective catalysts for the isomerization reaction of C8 aromatic compounds. This new preparation procedure imparts to the mordenite very improved geometric selectivity properties, which is reflected by a dramatic inhibition of undesirable secondary reactions such as the dismutation. This new modified mordenite further leads to selectivities, relative to the parasitic reactions cf dealkylation, which are less to those of the catalysts based on ZSM5. Thus, the result is solids which exhibit performances in isomerization of C8 aromatic compounds that are not only better than those of the mordenites of the prior art but also at least equivalent, and even superior, to the performances of the catalysts with a ZSM5 base.
The mordenite used in the catalyst of this invention is produced from a mordenite either of the type with small pores or the type with large pores.
The mordenite of the small pore type has a content by weight of sodium relative to the weight of dry mordenite generally between 4 and 6.5%, an overall Si/Al atomic ratio generally between 4.5 and 6.5, an elementary mesh volume generally between 2.76 and 2.80 nm.sup.3 (with 1 nm=10.sup.-9 m) and usually adsorbs only molecules of kinetic diameter less than about 4.4.times.10.sup.-10 m.
The mordenite of the large pore type is distinguished from that of the small pore type by the fact that it can adsorb molecules of kinetic diameter greater than about 6.6.times.10.sup.-10 m, therefore in particular the benzene molecules, in that its overall Si/Al atomic ratio is generally between 4.5 and 20 and in that its elementary mesh volume is usually between 2.74 and 2.79 nm.sup.3.
Before making the porous network of the mordenite selective by deposition of at least one metal from groups IIa, IVb, IIb, IVa, it is preferable to prepare first of all the H-shape of said mordenite with a content by weight of sodium relative to the weight of dry mordenite generally less than 2000 ppm, preferably 1000 ppm and, in a still more preferred manner, 500 ppm, an overall Si/Al atomic ratio between 6

REFERENCES:
patent: 3598724 (1971-08-01), Mulaskey
patent: 4501656 (1985-02-01), Dufresne et al.
patent: 4789655 (1988-12-01), Travers et al.
patent: 4902847 (1990-02-01), Juguin et al.
patent: 4935578 (1990-06-01), Dufresne et al.
patent: 4977121 (1990-12-01), Dufresne et al.
patent: 5077254 (1991-12-01), Travers et al.

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